FirstBits.com tells you how much of a Bitcoin address* you need to remember to uniquely identify it, usually only 4-7 characters. Share this 'firstbits' address and friends can find your whole address easily.

This is perfect for when the person paying you does not have immediate access to a computer and you trust them to pay you later.

Meeting someone to make a cash<-->BTC exchange? Just remember your firstbits. Say it and your partner can have your address in their client in seconds.

Here is another potential use. A shop displays an address for you to pay, you need only type the firstbits address into your phone, no need for typing 33 characters or taking a picture of a QR code.

I'm sure people will come up with uses I haven't thought of. I expect that the ability to pass addresses like this will open up some new possibilities.

*Your address must already be in the chain in order to have a firstbits address. You can send a token amount to yourself at any address to get it in the chain.

edit: Firstbits addresses are case-insensitive. This makes them a lot easier to remember and say and doesn't make them much longer on average.

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Specifying only the first 4 'bits' for addresses in my book mostly gives me a wrong result. This can be misleading and dangerous if users are not aware how it works.

It is not always 4 'bits', it depends on what other similar addresses have entered into the blockchain prior to that one. to find out how many your particular address needs, just type it in the box and it will tell you. As for it being dangerous to the naive user, thats the case with most things in life and is simply unavoidable.

Freemoney, let me know if my explanation is wrong. And thanks alot for making this, I've thought for a while something like this would be very useful!

Specifying only the first 4 'bits' for addresses in my book mostly gives me a wrong result. This can be misleading and dangerous if users are not aware how it works.

Good question.

You cannot guess your firstbits address. You need to enter it and find out (or search the chain yourself).

A firstbits address is the starting string that is sufficient to distinguish an address from all addresses before it in the chain. This way a firstbits can never change. Listing all matches would not tell you which was yours anyway.

Perhaps a warning is appropriate.

The main use I have in mind is a person learning one of their firstbits like they learn their phone number and using it for casual payments. It is not as great for people or situations where you need a new address each time.

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The main use I have in mind is a person learning one of their firstbits like they learn their phone number and using it for casual payments. It is not as great for people or situations where you need a new address each time.

Casual payments are definitely one of the first uses that comes to mind.

I know that one of my firstbits addresses is 18tkn. And I have memorized that address. Now, no matter where I am, if someone needs to pay me bitcoins, we can hop on the website, grab the full address, and they can pay me. I think this will work really great for casual payments, as FreeMoney said. Businesses could also potentially use it for payments, maybe people meeting up for craigslist transactions might find it handy, and certainly non-profits that take donations could make good use of it.

One caveat: you guys should not generate the FirstBits alias if the address is not found in the chain, and explain to the user why you can't give him his FirstBits alias.

If you generate a FirstBits alias for an address that hasn't been stored in the chain yet, there is a possibility of collision with someone doing the same thing.

edit:A nice use case for this will be combining it with the vanity addresses. If people could have a public address like "1joan" or similar, it could be terrific.

We do not generate the FirstBits address if the address is not found in the chain, for the very reason you mentioned. A bit of an explanation on that front might be warranted though - right now, we only tell the user that the address is not in the block chain, and there isn't any mention of why only blockchain addresses are included in the "About Firstbits" page either.

We do not generate the FirstBits address if the address is not found in the chain, for the very reason you mentioned.

Sorry, my mistake. I had clicked the "new" address button in the client to test. I didn't realize it had given me an address that had been used to collect change in a previous transaction Tried it again with a really new address, and it worked.

We do not generate the FirstBits address if the address is not found in the chain, for the very reason you mentioned.

Sorry, my mistake. I had clicked the "new" address button in the client to test. I didn't realize it had given me an address that had been used to collect change in a previous transaction Tried it again with a really new address, and it worked.

Oh, interesting... I didn't know that the client would do that either, good to know.

Specifying only the first 4 'bits' for addresses in my book mostly gives me a wrong result. This can be misleading and dangerous if users are not aware how it works.

It is not always 4 'bits', it depends on what other similar addresses have entered into the blockchain prior to that one. to find out how many your particular address needs, just type it in the box and it will tell you. As for it being dangerous to the naive user, thats the case with most things in life and is simply unavoidable.

Freemoney, let me know if my explanation is wrong. And thanks alot for making this, I've thought for a while something like this would be very useful!

That's right. I'd hate for people to use it wrongly, but I think warnings and extra explanation are just going to confuse anyone who can't do it correctly. I would like to hear other opinions though. In general if you aren't sure about what you are doing just don't press send on your client.

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